[h2]Basic requirements:[/h2]
-A decent computer: If you can't run a single instance of TF2 with low settings properly then this isn't for you. Just for reference I can idle with 7 accounts at the same time while playing other games like Resident Evil 5 or WoW with high settings on my 4GB RAM, GTX260 and Core2Quad Q9300 PC (before upgrade).

-2 or more (premium) TF2 accounts.

-The most important part: A trial or full version of Sandboxie. Warning: The trial only allows 1 sandbox. 1 sandbox+main=max 2 accounts at the same time.

[h2]Getting started:[/h2]
1.Download and install Sandboxie.

2.Delete the default sandbox and create a new one. Name it as you wish.

3.Right-click the sandbox and go to settings.

-Restrictions->Drop rights->Drop rights from Administrators and Power User groups must be unchecked.

-Resource Access->File Access->Full Access and add the HDD Steam is installed on or add specific Steam folder. <--VERY important step.

4.Right-click on your sandbox and Run Sandboxed->Run Windows Explorer and navigate to Steam and log on to your alt.

5.Apply your idling settings and run TF2. Then run Steam normally and idle with you main. If you get an error you have to wait until the first instance of TF2 finished loading.

Congratulations. You are now idling with 2 accounts simultaneously. If you want to trade between accounts just remove the idle settings and run TF2 normally add your idle account as friend and use the Steam trading feature. It lets you trade more than 8 items at once.

This is basically how multi-account idling works but there are a few problems. It's tedious to start TF2 by hand every time especially if you have more than 2 accounts and you have to wait until the first instance of TF2 finished loading until you can start a second one. If you already started multi-accounting then you might just go all the way and set up a farm!

-A full version of Sandboxie because the trial version only allows 1 sandbox.

[h2]Building the Farm[/h2] 1.Make a copy of Steam+TF2 files for each account and name the folders after your account or user name to avoid the loading issue.

Better method by raBBish, slightly modified by me. The old method involved copies of TF2 files which consumed a lot of HDD space. The new method uses links to one shared steamapps folder for all accounts and requires Windows 7 or Windows Vista.

1.Make a copy of Steam without the steamapps folder for each account.
a.Decide your main steamapps folder. Generally it should be the one with most games.
b.If you want, you can move the steamapps folder somewhere else and rename it (mine is D:\Games\Steam for example).
c.Remove all the other steamapps folders.
d.Open cmd.exe as an administrator.
e.Navigate into each Steam folder without steamapps and run the following:

Of course you have to replace the placeholders with you own names and directories.

If you run Idle.bat from step 5 it will launch TF2 instances in idle mode for every account you made batches for. It takes 14 minutes for me until all 8 accounts are fully loaded and idling. You may get freezes or slowdowns if your computer is too weak. The Login.bat from step 6 logs on your accounts and lets you start TF2 in normal mode for trading or whatever you want.

You are now set for advanced TF2 idling. Tweak around the batches and settings to get used to it and make your own modifications and/or improvements. Additional information for idling settings can be found here. I recommend using an idle config even with textmode because it lowers memory use even further. Here is what I use. Put it in each Steam folder Steam\steamapps\ACCOUNT\team fortress 2\tf\cfg and add +exec idle.cfg to every copy of step 3. Don't use it with your main account because it will mess with your video settings.

[h2]FAQ[/h2]
(WIP)

Q: One of my accounts lost connection while idling (NO STEAM LOGON). Do I have to restart the whole thing?
A: No. Right-click on the sandbox with the disconnected account and terminate programs. Open the Idle.bat and copy the line with the disconnected account. Paste the line into a new .bat file and run it.

Q: How can I idle or login to specific accounts?
A: Look above.

Q: What can I do about instance/blob error?
A: Make a copy of your Steam+TF2 files and run the copy in the sandbox.

Q: Is this bannable?
A: No.

Q: How can I tell if it's working?
A: By checking if it says X connected.

Q: I don't get any items. What's wrong?
A: Learn some patience. In most cases you're just unlucky or Valve item servers are down (most likely after updates). But just to be sure check your internet and Steam connection. Maybe you are drop capped.

Q: Does Steam block my IP if I run it multiple times?
A: Hell no. Why should it? I run 8 accounts from the same IP without problems. And what if your brother/sister/dog next door wants to play Steam games at the same time? Blocking IPs is a stupid thing to do for Steam.

Q: How can I prevent random people from joining my server?
A: Use a password by adding +sv_password xxx to the batches from step 3.

Q: Why does Steam validate/verify my files all the time?
A: If you use the mklink method only update TF2 with one account or you enter an endless update cycle. If you get this all the time even when running Steam normally consider redownloading.

Q: I get "Could not connect to Steam network" while login / "File is too large to copy into sandbox". What's wrong?
A: Check your resource access rights from step 3.

Steam.exe (main exception): Cannot open blob archive file:
CMUltiFieldBlob(mem-mapped file): Failed to open existing file, Win32 Error 32
"The process cannot access the file because it is being used by another process."

Steam.exe (main exception): Cannot open blob archive file:
CMUltiFieldBlob(mem-mapped file): Failed to open existing file, Win32 Error 32
"The process cannot access the file because it is being used by another process."

Technically you have to add funds to your wallet to be able to buy something from the store and the minimum it allows you to add is $5 so its $5 for a premium account, which in my opinion isn't a bad deal if you do want some extra items to turn into metal and all that jazz.

Edit:

Thinking about it, I might just spend $10 on two new accounts once summer crates start dropping and buying two summer keys on each account to make them premium. Seems like a good idea.

Edit:

Oh, and thanks for the guide OP! I tried using a guide from SPUF but it ended up not working.. I'll see if this one works!

That's what I thought, but in the case you shouldn't put a trial version as a requirement. Well, only if people only got 2 accounts... But, you need to imply more strongly they'll be needing the full version. Of course without implying black buisness is required too much ;)

Considering that, the majority of people who care about idle accounts got more than one.

That's what I thought, but in the case you shouldn't put a trial version as a requirement. Well, only if people only got 2 accounts... But, you need to imply more strongly they'll be needing the full version. Of course without implying black buisness is required too much ;)

Considering that, the majority of people who care about idle accounts got more than one.

That's what I do on my main. I always hit the drop cap just from playing.

However, considering how cheap idle accounts are these day, I'd highly suggest getting some. They will have made their own value back in 1-3 weeks(New accounts got much better Hat drop rates) if you like selling items. If not, and you want to get the most fun out of TF2, I'd STILL suggest it.

I for example, thanks to my idle accounts, was able to craft ALL the new Über update weapons right away after the update. That means I don't have to bend down to people overcharging, I can have fun before weapons become nerfed, and I even end up getting some extras I can give to friends(FHAIT too) so they can take part in the fun too.

I don't regret purchasing my idle accounts, they've been totally worth it, and I even paid 7.50 Euro for each of them(I got 3).

I tried running two accounts (Mine and an alt) with the alt boxed and I get this whenever I try to run TF2 from my account:
I managed to get it to work once during the last double drop week but I have completely forgotten how. Can anybody help?

I tried running two accounts (Mine and an alt) with the alt boxed and I get this whenever I try to run TF2 from my account:
I managed to get it to work once during the last double drop week but I have completely forgotten how. Can anybody help?

Tested it for about two hours, didn't find anything on any of the accounts I used. I followed all of the directions and the textmode idle itself worked properly. I started each account normally and did not receive a single item. Did I do something wrong?

Tested it for about two hours, didn't find anything on any of the accounts I used. I followed all of the directions and the textmode idle itself worked properly. I started each account normally and did not receive a single item. Did I do something wrong?

A very useful tutorial but its much more complicated (to me anyway but thats because I am horrible with things like this) than my method of idling on my main the first two days, idling on my alt the next two days then transferring them using two computers. But this is very helpful to those with only 1 account.